This invention relates to a device for detecting a freeze or thaw condition. More particularly, it relates to an improved freeze-thaw indicator utilizing a liquid-filled frangible ampul, with one side weakened with respect to the other for reliable indication.
Foods, pharmaceuticals, and other items are often frozen in order that they may be preserved for consumption sometime later. If these items are thawed, even for a short period of time, they may be subject to spoilage and, at the very least, their characteristics may change so that they are undesirable for later use. Conversely, there are other materials which are rendered relatively useless if the ambient temperature goes below the freezing point of water. It is, therefore, desirable to provide an indicator device which will accurately show whether or not an item or environment has gone through the freezing point of water or some other liquid.
One example of a device which has been used in the past as a freeze-thaw indicator is described in U.S. Pat. No. 3,177,843, issued Apr. 13, 1965, and invented by R. S. Geocaris. The Geocaris patent shows a device utilizing a frangible capsule which is located adjacent to a liquid absorbent material. The frangible capsule is filled with colored water and when the colored water freezes, the capsule will break. When the water subsequently thaws, the coloration will be absorbed by the absorbent material to indicate that a freeze or thaw has occurred. One of the problems associated with the device set forth in the Geocaris patent is that the use of a coloring additive in the water changes the freeze characteristics of the water such that it may not freeze near 0.degree. C. A further problem with the Geocaris device is that the capsule is a concentric device. The freeze expansion forces would be applied equally to all sides which may cause the capsule not to break. Another shortcoming with the Geocaris device is how to fill the capsule with enough liquid such that the water to ice expansion will be sufficient to break the capsule.
Another problem in prior art freeze-thaw indicators is the protection of the frangible capsule during a non-freeze condition; that is, if the capsule is not adequately protected from mechanical shock, it may be broken, thereby giving a false indication. It is, therefore, desirable to provide a freeze-thaw indicator which overcomes these and other deficiencies of the prior art.